Spark plug



Jan. 7, 1930. RABEZZANA 1,742,784

SPARK PLUG Filed May 1925 gwuewio a 66/52 flzmiza 553m a If;

Patented Jan. 7, 1930 UNITED STATES PATENT OFFICE HECTOR RAIBEZZANA, OI FLINT, MICHIGAN, ASSIGNOR TO A C SPARK PLUG COMPANY, 01 FLINT, MICHIGAN, A COMPANY OF MICHIGAN I SPARK IPLUG Application filed May 2 In low compression engines relatively low temperatures are'attained in the combustion chamber. With the ordinary type of spark plug this frequently results in the insulator eing maintained at such low temperatures that the particles of carbon and oil which collect upon it are not burned off but form an. accumulation which eventually short circuits the plug.

To overcome this difficulty I have so treated the surface of my insulator as to enable it to attain the higher temperatures requisite for the burning ofl' ofcarbon. I have accomplished this by substituting for the glaze heretofore used a special glaze distinguished by the fact that it has a greater capacity for the absorption of heat and therefore is enabled' to reach a higher temperature.

Figure 1 shows a conventional spark plug insulator treated with my special glaze; while Figure 2 shows a spark plug insulator of the ribbed type similarly coated.

Insulators ofspark plugs now upon the market are customarily provided with a glaze which gives to the insulators a smooth finish to which carbon and oil particles will not readily adhere. In some cases the insulator is first burned and then a low melting point is applied by spraying 'or,

dipping and the insulator is again baked but at a temperature which-is merely sufficiently high to melt the glaze. In other cases the glaze is applied before firing and the burning of the body of the insulator and the glaze is done at the same time. This necessitates the employment of a glaze having a high melting point. A typical glaze employed where the last named method is used is composed of the following ingredients Parts Flint Clay L Feldspar 34 Lime or whiting As previously stated my invention consists in the application to the body of the insulator of a glaze possesing the special characteristics of greater capacity for'the absorption of heat. In Figure l I have illustrated a spark plug 1925. Serial No. 27,505.

insulator of conventional design provided with a special glaze indicated at 2. I have found that, in general, dark colored glazes teristic of being relatively good absorbers of heat and it is to be understood that my inven tion is not limited to the use of this particular compound.

With a glaze of the desired character applied, the surface of the insulator reaches a sufficiently high temperature to affect a burning off of the oil and carbon which tends to accumulate upon it.

The insulator shown in Figure 2 is of the so-called carbon-prooftype the ribs or fins tate \ It is to be understood of course that my invention is not limited to the use of a glaze. of any particular composition but resides mainly in the conception of the adaptability of glazes possessing good heat absorbing qualities for securing the result desired,that is, the burning off of deposits of oil and carbon.

ing qualities which is used in describing the coating in the claims, glaze possessing markedly greater heat absorbing qualities than the glazes now used, of which the one given in the specification is .a typical example. One example of a suitable glaze composition coming within the scope of my invention consists of flint china clay 20%, feldspar 14%, cobalt oxide or manganese oxide 1%. In this composition the clay performs its usual function of causing the glaze to adhere to' the porcelain.

By the phrase relatively high heat absorb- I refer to a coating or I claim: 1. A spark plu insulator comprising a ceramic body 0 high thermo-dielectric strength having the ortion which projects into the combustion dhamber provided with a substantially black glaze to increase the surface temperature during the operation of the plug and facilitate the burning oif of carbon.

2.. A spark plug insulator comprising a ceramic body of high thermo-dielectric strength having the portion which projects into the combustion chamber provided with a substantially black glaze containing cobalt oxide.

3. A spark plug insulator comprising a ceramic body of high thermo-dielectric strength having the portion which projects into the combustion chamber provided with a substantially black glaze consisting of flint, feldspar, and cobalt oxide.

4. A spark plug insulator comprising a porcelain-like ceramic body provided with a substantially black heat absorbing glaze.

5. A spark plug insulator comprising a ceramic body of high thermo-dieleotric strength having the portion which projects into the combustion chamber provided with a substantially black heat absorbing surface to increase the surface temperature during operation of the plug, and facilitate the burning off of carbon.

In testimony whereof I afiix my signature. HECTOR RABEZZANA. 

